1. Field of the Invention
This invention relates to a process for preparing acrylonitrile by the vapor-phase catalytic ammoxidation of propylene. More specifically, the invention relates to a process for preparing acrylonitrile by the vapor-phase catalytic ammoxidation of propylene using a multiple promoted iron oxide-antimony oxide catalyst having a specific catalytic structure.
2. Description of the Prior Art
The output of acrylonitrile by the vapor-phase catalytic ammoxidation of propylene now amounts to a very large figure, and even a slight increase in the yield of acrylonitrile gives rise to a great economical advantage. Incessant efforts have therefore been made to develop catalysts of good performance for the production of acrylonitrile. In view of environmental problems, too, it has been strongly desired in recent years to provide catalysts which can be used to produce acrylonitrile in a higher yield and cause a reduction in the formation of by-products that are difficult to treat.
Well-known catalysts effective for the production of acrylonitrile by the vapor-phase catalytic ammoxidation of propylene are the catalyst composed mainly of bismuth phosphomolybdate described in U.S. Pat. No. 2,904,580 and the catalyst composed mainly of an oxide of antimony and an oxide of uranium described in U.S. Pat. No. 3,198,750. These catalysts have been used commercially, but have not been found satisfactory with respect to the yield of acrylonitrile. Catalysts which bring about higher yields have also been proposed.
Further, an iron oxide-antimony oxide mixed catalyst is useful in the vapor-phase catalytic ammoxidation of propylene as disclosed in Japanese Patent Publication No. 19111/'63 (Japanese Pat. No. 420,264), U.S. Pat. No. 3,197,419 and British Pat. No. 983,755. Moreover, improved results are obtained by the addition of particular additives to such a catalyst as disclosed in U.S. Pat. Nos. 3,338,952, 3,542,843, 3,591,620, 3,668,147 and 3,716,496. These catalysts, however, have not proven to be entirely satisfactory with respect to the yield of acrylonitrile and in other properties.
With a view toward further improvements, the properties of the catalysts disclosed in U.S. Pat. Nos. 3,668,147 and 3,716,496 were discovered, and it was found that when these catalysts have a specific catalytic structure and contain a Me component (i.e., V, Mo and W) in an amount larger than that disclosed in these patents, further improvements in the production of acrylonitrile were exhibited.